1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus and in particular to an ultrasonic diagnostic apparatus for evaluating mechanical characteristics of bone.
2. Description of the Related Art
Easy and quantitative measurements of bone strength are desired for diagnosing bone metabolic diseases such as osteoporosis, judging fracture risk, and quantitatively diagnosing bone union after treatment of bone fracture.
The evaluation of bone formation and bone union depends largely on an X-ray photograph, but it is difficult to quantitatively diagnose the bone strength with an X-ray photograph. As a method of measuring bone strength, conventionally, there is known a strength test of a sample bone of a measurement target. However, in this method, it is necessary to apply an extraction operation of a sample bone, and thus, the method is invasive. As a method of measuring an amount of bone and a bone density, the use of devices such as X-ray CT and DXA (dual-energy x-ray absorptiometry) has been put in practice. However, these devices only measure the amount of bone and cannot provide an evaluation of the bone strength. Moreover, as X-rays are irradiated in these methods, these methods cannot be considered as non-invasive.
Other attempts to quantitatively evaluate the bone strength include a strain gauge method in which a strain gauge is mounted on an external fixtator and the strain of the external fixtator is measured, a vibration wave method in which a vibration is applied to a bone from the outside and a characteristic frequency is evaluated, and an acoustic emission method in which acoustic waves generated by a bone which has reached the yield stress are detected. These methods, however, have various problems in that there is a limitation to the treatment to which these methods can be applied, that invasion must be applied to the bone, and that the precision is insufficient.
Attempts have been made to analyze fine structures of the bone using ultrasound, but the relationship between the result of this analysis and the bone strength is not yet known (refer to, for example, Japanese Patent Laid-Open Publication No. Hei 9-84788).